Poster Presentation
ALMA Observations of Spiral Accretion Flows Towards Extremely Young Protostars
Presenter: Pou Ieng Cheong (NTHU)
Studying the accretion flows toward extremely young protostars is an important step toward understanding how the protostellar disks are assembled in the early stage of star formation. The accretion flows are commonly seen in the MHD simulations; however, they are rarely observed due to their low intensity. Here we report our discovery of large-scale accretion flows (∼ 3600 AU long) around an extremely young protostar VLA1623A with a protostellar disk likely just formed with Atacama Large Millimeter/submillimeter Array (ALMA) observations of C18O (J=2-1) emission. We identify four groups of stream-like structures at different velocity ranges from the three-dimensional Position-Position-Velocity data cube using “Dendrogram" algorithm (Goodman et al. 2008). Some of these stream-like structures are likely to be outflows or the wall of outflow cavities, but we find that two of our identified “branches" can be matched well with the CMU model (Ulrich 1976; Cassen & Moosman 1981) which describe the velocity structure of the accreting gas with constant angular momentum. The best fitting results give the centrifugal radius of 150 AU which is the same size of the Keplerian disk estimated by Murillo et al. (2013). With the CMU model, we are able to produce a three dimensional (Position-Position-Position) view of the accretion flows which shows that the thickness of the Keplerian disk at the boundary is less than 30 AU.
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